After an hour of allsorts of ways to get around the lorry gate bug, i think i've sorted it.
If the lorry don't crash through the gate, pull up the console by pressing "@" key, then type "Restart" (without the ")in the console and press return.
The level will reload, now head back to the gate and the lorry crashes through the gate
.
I did not have cheats/trainer running when i did this, and i walked between the wall on the left and the black car on the right as told by "MrLipid" in the post above.
Hope that helps, i'm off to play some more "You Are EMPTY".